1. Field of the Invention
The present invention relates a control device for a vessel equipped with an exhaust heat recovery system and the vessel equipped with the control device. The exhaust heat recovery system comprises an internal combustion engine and a shaft generator connected to the internal combustion engine via a shaft and a feedback control device which performs feedback control of the rotation speed of the internal combustion engine based on the fuel injection amount needed for the internal combustion engine to a target rotation speed of the internal combustion engine.
2. Description of the Related Art
As an exhaust heat recovery system for vessels, there is a power generation system wherein a steam turbine is driven by performing heat exchange with exhaust gas discharged from a main engine with use of a exhaust gas economizer using the exhaust gas of the engine and a system wherein the power is generated by rotating the shaft generator by engine output so as to compensate for electric load within the vessel. These types of systems have been proposed in view of saving energy in the vessel. For instance, Patent Document 1 (JP2007-001339A) discloses the system wherein the exhaust gas of the engine is utilized to drive the gas turbine and to partially compensate for the electric load within the vessel.
In the energy recovery system equipped with the gas turbine, the distribution of the power is decided among a steam turbine, a gas turbine, and a shaft generator depending on the engine load.
A structure of a conventional exhaust heat recovery system equipped with a gas turbine is illustrated in FIG. 7. The conventional exhaust heat recovery system of FIG. 7 comprises an engine 51 for propelling the vessel, a shaft generator 52 for actuating the engine 51, a propeller 53 being rotated by the output of the engine 51, a supercharger 54 for compressing the air to be supplied to the engine 51, a cooler 55 for cooling the air from the supercharger 54, electric power 61 within the vessel generated by the shaft generator 52, generator 58, and an auxiliary generator 60.
Further, in the vessel, an exhaust gas economizer 59 is provided to generate steam. The exhaust gas discharged from the engine 71 is supplied to the exhaust gas economizer via the supercharger or the gas turbine 56. The steam obtained in the exhaust gas economizer 59 is used to actuate the steam turbine 57 and then the generator 58 is driven by the steam turbine 57 and the gas turbine 56.
The water and steam lines are indicated with dotted lines in FIG. 7. The steam returns to the water in a condenser 62 arranged on a downstream side of the steam turbine 57. Subsequently, the water is heated by the heat of the cooler and the heat used for cooling walls of the engine 51 and then supplied to the exhaust gas economizer 59. The water evaporates, thereby generating the steam.
In reference to FIG. 8, it is explained hereinafter how to control the fuel injection amount for the vessel equipped with the above exhaust heat recovery system.
In FIG. 8, a target rotation speed of the propeller is given to a control unit 41. The control unit 41 converts the target rotation speed of the propeller into a fuel injection amount and sends the target fuel injection amount to a fuel injection device 42 of the engine. Next, assist torque from the shaft generator is added to an engine output corresponding to the fuel injection amount and then the vessel resistance is subtracted to perform calculation 43 of the rotation speed of the propeller. The difference between the target rotation speed of the propeller (the command rotation speed of the propeller sent from the operator) and the actual output of the propeller is obtained in the subtractor 44. The actual output of the propeller is corrected to the target rotation speed of the propeller having been subtracted. The corrected target rotation speed of the propeller is obtained based on the subtracted correction value by controlling the injection amount based on the corrected value having been subtracted. As a result, the propelling responsiveness of the vessel is improved.
In contrast, Patent Document 2 (JP2008-126771A) discloses a steering device for a vessel that improves a turning responsiveness of the vessel. According to Patent Document 2, the steering device for the vessel comprises a propulsion unit arranged at the stern thereof, a control unit for controlling thrust of the propulsion unit, and a turning unit being driven by an electric actuator for turning the vessel, an handle connected to the electric actuator electrically so as to send a drive signal in correspondence with the operation amount to the electric actuator and being operated by a vessel driver, wherein the control unit comprises at least one of a steering state detector for detecting a state of the handle operation, a running state detector for detecting a running state of the vessel, a propulsion unit state detector for finding a state of the propulsion unit such as the number of the units mounted on the vessel, and a actuator state detector for detecting a state of the electric actuator, and wherein the steering device further comprises a propulsion calculation unit for calculation a target propulsion based on a detection value obtained by at least one of the above units, and a propulsion control unit for controlling the propulsion of the propulsion unit according to the target propulsion calculated by the propulsion calculation unit.
However, the device of Patent Document 2 improves the turning responsiveness of the vessel and does not enhance the propelling responsiveness of the vessel or control the condition of the engine in response to the rotation speed of the propeller.
The engine output is determined by adding the propeller and the electric power within the vessel. In the past, the engine output, i.e. the fuel injection amount of the engine, was not controlled with consideration of both the propeller and the electric power within the vessel.
Further, the operator sends the command rotation speed of the propeller as a command so as to control the fuel injection amount of the engine based on the command rotation speed. Furthermore, a generator (a shaft generator) is arranged on the output shaft of the engine if necessary. The propeller is rotated on the engine shaft and thus the speed of the vessel is essentially determined by the rotation speed of the propeller, i.e. the rotation speed of the engine. However, the disturbance resistance such as the conditions of the wave is ultimately considered. In the past, the fuel injection amount was adjusted in an engine room of the vessel to achieve a target vessel speed. And the engine control was not performed with consideration of the vessel speed.
In the vessel with the exhaust heat recovery system, the electric power is supplied by the gas turbine, the steam turbine, the shaft generator and so on. Thus, when the rapid drop in the load within the vessel generates surplus electricity, the shaft generator is used as a generator so as to consume the surplus electricity and also to assist the driving power of the vessel. Therefore, when the rapid drop in the load within the vessel generates surplus electricity, there is torque turbulence of the assist torque from the shaft and thus the vessel is rapidly accelerated.